Process and system for producing nuclear spin polarized xenon gas

ABSTRACT

The present invention provides producing method and producing apparatus in which polarized xenon gas of high concentration is obtained without being frozen, and polarized xenon gas can be produced continuously. A glass cell having solid rubidium and solid xenon filled in vacuum is heated to be gas xenon and gas-liquid mixed rubidium, to which a magnetic field is applied to irradiate a laser beam thereby obtaining polarized xenon gas of high concentration.

TECHNICAL FIELD

This invention relates to producing method and producing apparatus ofnuclear spin polarized xenon gas, and more specifically, relates toproducing method and producing apparatus of nuclear spin polarized xenongas capable of producing a polarized nuclear spin useful for NMR.MRIapparatus with high concentration and continuously.

BACKGROUND

It has been recently reported that when xenon gas with a nuclear spinpolarized (nuclear spin polarized xenon gas) is applied to NMR.MRImethod, detection sensitivity is enhanced rapidly.

Being polarized termed herein is that distribution of the spin numberoccupying energy order of nuclear spins of an atomic nucleuscorresponding to the orientation state with respect to the metal staticmagnetic field is extremely one-sided.

Rare gas having the polarized state is obtained in the procedure suchthat circularly polarized excitation light is irradiated on gas havingrare gas including a single atomic molecule having a nuclear spin ofspin quantum number ½ such as xenon-129 (¹²⁹Xe), helium-3 (⁹He) or thelike mixed with alkali metal vapor such as rubidium, cesium or the likewhereby electron in the base state order of rubidium or the like isexcited by light absorption in the base state order and returned to thebase state order after passage of the base state order, at which time itis transited with high probability to one order of electron orders outof the base state orders whose degeneracy is released magnetically bythe magnetic field applied from outside to prepare the state that anelectronic spin polarization degree of a rubidium molecule or the likeis high, and the rubidium or the like in the high polarization statecollides with rare gas such as xenon, at which channel the highpolarization state of rubidium or the like moves to a nuclear spinsystem of rare gas such as xenon. This channel is generally calledoptical pumping.

In the conventional polarized rare gas producing apparatus, a mixed gasof rare gas and alkali metal vapor is confined into an optical reactionvessel, to which irradiation of excited light and application ofmagnetic field are carried out. For example, there is a producingapparatus, for the purpose of using polarized helium-3 of high densityas a neutral polarizer, in which a mixed gas of helium-3 gas andnitrogen gas and alkali metal are confined into a cylindrical glassample (for example, see M. E. Wagshul and T. E. Chu P P, Phy, Rev. A40,4447 (1989)).

On the other hand, there is an apparatus in which for example, 1% ofxenon is mixed with buffer gas of helium of 10 atmospheric pressure orso, introduced into a cylindrical glass vessel, irradiated, polarized,and guided into Dewar cooled by liquid nitrogen from a gas outlet of thevessel, and polarized xenon is formed into a solid, which is separatedwhereas the remaining helium gas is discharged from a vent line (Forexample, see B. Driehuys, G D. Cates, E. Miron, K. Sauer, D. K. Walterand W. Happer, Appl. Phys, Lett. 69, 1668(1996).

In any of those apparatuses as noted above, operation for enhancing thepolarization rate is carried out by receiving a laser beam in the statethat rare gas or the like is stayed in an optical reaction vessel. Whenthe polarization rate was enhanced, the temperature is cooled to a roomtemperature, and being used as a neutral polarizer as it is, orpolarized xenon 129 once solid-separated within Dewar is heated againinto gas, and transferred to a separate vessel for use in measurement ofNMR or the like.

However, in the above-mentioned conventional method, for facilitatingpolarization, xenon is diluted, for example, to helium 2% xenonconcentration or so and polarized, gas containing produced xenon isfrozen with liquid nitrogen, which is heated to remove only the xenon toproduce high concentration xenon gas, thus posing a problem that workefficiency is extremely poor. In addition, in the conventional apparatusin which gas or the like is stayed and polarized, since polarized gascannot be generated continuously, polarized gas is taken out into aseparate vessel every time and carried to NMR apparatus, thus takingtime, and posing a problem that the polarization rate reduces duringsuch a period of time as described.

This invention has been accomplished in view of the foregoing, and hasits object to provide producing method and producing apparatus capableof obtaining polarized xenon gas of high concentration without beingfrozen, and capable of generating polarized xenon gas continuously.

It is a further object of this invention to provide producing method andproducing apparatus of a glass cell in which metal rubidium and xenongas used for the above-described producing method and producingapparatus are solidified and sealed under the absence of oxygen.

DISCLOSURE OF THE INVENTION

The producing method according to claim 1 out of the inventions suitedfor the aforementioned objects is characterized in that a glass cellhaving solid rubidium and solid xenon filled in the pressure reducingstate of being absent in oxygen is heated to be gas xenon and gas-liquidmixed rubidium, to which a magnetic field is applied to irradiate alaser beam. It is noted that being absent in oxygen termed herein ismeant not to oxidize solid rubidium, and the presence of a fine amountof oxygen to a degree that even if solid rubidium is oxidized, reactionis not affected, is allowed.

When the thus produced nuclear spin polarized xenon gas is taken out,pressure naturally lowers and air flows backward into the glass cell.Therefore, xenon polarized gas is taken out while introducing xenon gasso as to maintain fixed pressure. Further, by doing so, polarized xenongas can be produced continuously.

Preferably, it is constituted so that in replacing a xenon gas supplydevice, the xenon gas supply device side is made to be a primary sidethrough a first air operate valve, and the xenon gas introducing side ofthe glass cell is made to be a secondary side, and vacuuming of theprimary side piping and pressurization-leaving by nitrogen gas arerepeated automatically more than three times.

Preferably, in replacing the glass cell, vacuuming of piping from theprimary side piping, the secondary side pipe and the primary side pipeto a valve on the polarized xenon gas take-out side communicated througha second air operate valve and pressurization-leaving by nitrogen gasare repeated automatically more than three times.

A producing method of a glass cell according to the present invention ischaracterized in that a chamber housing therein rubidium filled into aglass vessel and said glass cell are connected so that they arecommunicated by piping, said piping is exhausted by a vacuum generator,after which a glass vessel filled with rubidium is broken to heat metalrubidium, piping and glass cell, rubidium of gas is made present withinthe piping and glass cell, then said glass cell is cooled, metalrubidium is precipitated as a solid into the cooled portion, xenon gasis introduced into the glass cell and closed, and the glass cell iscooled to solidify xenon within the glass cell.

A producing apparatus of the present invention is characterized bycomprising means for heating a glass cell having solid rubidium andsolid xenon filled in the pressure reducing state of being absent inoxygen to be gas xenon and gas-liquid mixed rubidium, and means forapplying a magnetic field to the glass cell to irradiate a laser beam.

Further, preferably, there comprises means introducing xenon gas whiletaking out the produced nuclear spin polarized xenon gas, and pressureregulating means for controlling said operation so that pressure may notdrop.

Preferably, a xenon gas supply device side is made to be a primary sidepiping through a first air operate valve, piping extended up to a valvefor introducing xenon gas into a glass cell is made to be a secondaryside piping, branched pipings connected to said primary side pipingthrough a second air operate valve, one of said branched pipingsreaching a vacuum generator and the other reaching a valve on the xenongas taking-out side of said glass cell, and pressure regulating meansfor regulating pressure introduced into the glass cell is provided onthe primary side piping.

A producing apparatus of a glass cell according to the present inventioncomprises piping connected so that a chamber housing rubidium filledinto a glass vessel and the glass cell are connected, means forvacuuming the piping, means for breaking glass having rubidium filledin, means for heating metal rubidium, piping and a glass cell, and meansfor cooling the glass cell and precipitating metal rubidium on thecooled portion.

In summary, the gist of the present invention lies in that xenon isfilled into the glass cell having metal rubidium adhered thereto heatedto irradiate a laser beam thereby obtaining polarized xenon gas of highconcentration without being frozen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing a producing apparatus of aglass cell having rubidium and xenon filled therein according to thepresent invention.

FIG. 2 is a sectional view showing the state that rubidium and xenon arefilled in, and thereafter a glass cell is closed and sealed.

FIG. 3 is a structural view showing one embodiment of the producingapparatus according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, the embodying form of the present invention will bedescribed with reference to the drawings.

FIG. 1 shows a producing method (apparatus) of a glass cell havingrubidium and xenon filled in, in which a vacuum pump 5 and a xenon gassupply line 6 are connected to piping 4 connecting a metal rubidium 1enveloped with glass housing chamber 2 and a glass cell 3. When rubidiumcomes in contact with air, it is oxidized and changed into oxide ofrubidium, and therefore in case of purchasing it from makers, it isfilled in glass as described above. It is noted that in this state, avalve Vxe, a valve V1 and a valve V2 are closed.

If a valve Vp is opened, in the state that the valve Vxe is closed, toexhaust by the vacuum pump 5, air in the piping 4 and the glass cell 3is exhausted. When, in this state, glass in which rubidium is filled isbroken, metal rubidium will be present in vacuum, thus not beingoxidized. A magnet enveloped with glass is also filled in the metalrubidium 1 housing chamber 2, which is moved by the magnet from outsideto be placed in contact with metal rubidium 1 to break glass. Next, themetal rubidium 1, glass cell 3 and piping 4 are wholly heated. It issuggested that a heating temperature is not less than a melting point(about 40° C.) of rubidium, and is a temperature that rubidium assumes agas-liquid mixed state in which liquid and gas of a vapor pressureportion at that temperature are present with high concentration. Morespecifically, preferably, 130˜180° C., particularly preferably, near150° C.

Then, when only a part of glass cell is cooled, rubidium in the gasstate is solidified on only the cooled part and separated as shown inFIG. 3.

Then, when the vacuum pump 5 side valve Vp is closed and Vxe is opened,gaseous xenon is introduced into the glass cell 3. Next, when Vxe isclosed, and the whole glass cell 3 is cooled with liquid nitrogen, xenonis turned to solid. Originally, since xenon is introduced into solidrubidium confined in vacuum, if xenon is solidified, the glass cellassumes a pressure reducing state (vapor pressure at a liquid nitrogentemperature).

In this state, if a portion 8 depicted in FIG, 2 is heated and molten byoperation of a burner, the glass cell 3 having solid rubidium and solidxenon filled in is obtained.

Using the glass cell, and there is constituted as shown in FIG. 3, andwhen the temperature of the glass cell 3 is elevated, preferably, to50˜180° C., particularly preferably, near 120° C., the glass cell willinternally be xenon gas and gas-liquid mixed rubidium. In this state, ifa magnetic field is applied to irradiate laser, xenon gas will benuclear spin polarized xenon gas in scores of minutes.

Then, as shown in FIG. 3, the valves V2 and V3 are opened, and polarizedxenon gas is collected by a polarized xenon gas collecting cylinder 9,and at the same time, the valve V1 is opened to introduce xenon gaswhile regulating pressure by an auto pressure regulator (APC) 10 so thatpressure may not drop. When polarized xenon gas in the glass cell 3 istaken out, pressure lowers and the air back flows, because of which thepressure-regulate xenon gas is introduced as described above. It isnoted that in this state, air operate valves AV6, AV1 and AV3, andvalves V1. V2 and V3 in FIG. 3 are opened.

Then, the valves V1 and V2 are closed, the whole glass cell 3 is cooledwith liquid nitrogen, and after xenon is solidified, the glass cell 3 isheated to produce polarized xenon gas by the same operation as mentionedabove. In this manner, it can be produced repeatedly continuously tillrubidium as a catalyst is gone.

As shown in FIG. 3, xenon gas from a xenon cylinder 11 is introducedfrom the valve V1 of the glass cell 3 passing though an air operatevalve (AV1), an auto pressure regulator (APC) 10 and a first air operatevalve (AV3). In this embodiment, since pressure for taking out polarizedxenon gas is 1.5 atmospheric pressure or so, pressure of xenon gas isregulated to the same 1.5 atmospheric pressure or so by APC10. In FIG.3, valves V1˜V4 are constituted by glass valves because polarized gascomes in contact, and because if glass is not employed, polarized xenongas returns to xenon gas. Accordingly, other portions within piping withwhich polarized xenon gas contacts are also glass (pyrex).

Nitrogen gas and xenon gas are dropped down to pressure of 1.5atmospheric pressure or so by pressure reducing valves (REG 2 and REG1), respectively.

In the above-described reaction, it is necessary that air may not enterat all the glass cell. Because even if a small amount of air is mixed,the rubidium catalyst is oxidized, resulting in not exhibiting thecatalyst function.

Air is mixed in at the time of replacing a cylinder and at the time ofreplacing a glass cell, in which case, air is prevented from mixing intothe glass cell in the following manner.

In case of replacing a xenon cylinder, air is mixed into piping betweenan original valve 13 of the cylinder, an air operate valve (AV1) and anair operate valve (AV6). For removing the air, a vacuum pump (P) 15 isturned on, an air operate valve (AV1) and air operate valve (AV2) and asecond operate valve (AV4) are opened to vacuum piping on the primaryside, and the state is left as it is for fixed time while detecting apressure reducing degree by a pressure transmitter ((PT1). Through thefirst air operate valve (AV3), the xenon gas supply device side is madeto be a primary side, and the xenon gas introducing side of the glasscell is made to be a secondary side.

Then, the second air operate valve (AV4) is closed to pressurize heinterior of piping on the primary side with nitrogen gas. The pressureon the primary side is left for fixed time preset while detecting it bythe pressure transmitter (PT1). Then, the step is again repeated forvacuuming again the interior of piping on the primary side andpressurizing the interior of piping on the primary side with nitrogengas to leave it. Preferably, it is possible to prevent oxygen frommixing into the glass cell by repeating the step more time 10 times.

When the glass cell is replaced, air is mixed into the piping betweenpiping to the manual valve V1 at a glass cell inlet on the secondaryside in communication with piping on the primary side through the firstair operate valve (AV3), the manual valve V2 for taking out polarizedgas, the valve V3 or controlling the flow into the collecting potion,and the valve V4 for controlling the communication with the vacuum pipe.

The valve V4 and the second air operate valve (AV4) (controllingcommunication between piping on the primary side and he vacuum pump) areopened to vacuum the interior of piping of the air mixing portion. Then,the first air operate valve from the both cylinder 11,12 (AV3)connecting pipings on the primary side and secondary side, and the valveto the first air operate valve (AV3) are opened to pressurize piping onthe primary side and piping on the secondary side with nitrogen gas, andall the valves are closed for pressurization-leaving. Then, the step isrepeated for opening the first air operate valve and the second airoperate valve, vacuuming similar to that mentioned above, andpressurization-leaving. Preferably, it is possible to prevent oxygenfrom mixing into the glass cell by repeating the step more than 10times. Since the pressure transmitter (PT2) is disposed on piping on thesecondary side, vacuuming and pressurization-leaving are performed forfixed time pre-set while sensing pressure. The air operate valve (AV5)in FIG. 3 is a valve for releasing gas when the interior of the primarypiping is in the pressurizing state, which is however not used in theabove-described operation.

In FIG. 3, while nitrogen and xenon gas are supplied from the cylinder,well known other gas supply devices will suffice.

According to the present invention, reaction is done with highconcentration such as xenon gas 80˜100% (remainder, nitrogen gas) tothereby obtain polarized xenon gas, thus obtaining polarized xenon gasof high concentration without carrying out treatment such as solidifyingafter being polarized.

Further, vacuuming the interior of piping and pressurization-leaving canbe carried out many times to prevent air from flowing into the glasscell.

As described above, according to the present invention, since xenon gasof high concentration can be used to produce polarized xenon gas of highconcentration, trouble of concentrating by freezing after production asin prior art can be eliminated.

Further, xenon gas as raw material is regulated in pressure andintroduced while taking out polarized xenon gas, whereby back-flow ofair is prevented, and polarized xenon gas can be produced continuously.

Furthermore, vacuuming the interior of piping and pressurization-leavingare carried out repeatedly to thereby sufficiently enable purging theinterior of piping, and so, it is possible to prevent mixing of air inhe reaction glass cell, and to extend the life of the rubidium catalyst.

Accordingly, it is expected to utilize the invention as producing methodand producing apparatus of producing polarized nuclear spin polarizedxenon gas useful for NMR.MRI apparatus with high concentration andcontinuously.

1. A producing method of nuclear spin polarized xenon gas characterizedin that a glass cell having solid rubidium and solid xenon filled in thepressure reducing state of being absent in oxygen is heated to be gasxenon and gas-liquid mixed rubidium, to which a magnetic field isapplied to irradiate a laser beam.
 2. The producing method according toclaim 1, wherein xenon gas is introduced so as to maintain fixedpressure while taking out the nuclear spin polarized xenon gas producedby irradiating the laser beam.
 3. The producing method according toclaim 2, wherein in replacing a xenon gas supply device, the xenon gassupply device side is made to be a primary side through a first airoperate valve, and the xenon gas introducing side of the glass cell ismade to be a secondary side, and vacuuming of the primary side pipingand pressurization-leaving by nitrogen gas are repeated automaticallymore than three times.
 4. The producing method according to claim 3,wherein in replacing the glass cell, vacuuming of piping from theprimary side piping, the secondary side pipe and piping to a valve onthe polarized xenon gas take-out side communicated through a second airoperate valve with the primary side pipe and pressurization-leaving bynitrogen gas are repeated automatically more than three times.
 5. Aproducing method of a glass cell having solid rubidium and solid xenonfilled in vacuum characterized in that a chamber housing thereinrubidium filled into a glass vessel and said glass cell are connected sothat they are communicated by piping, said piping is exhausted by avacuum generator, after which a glass vessel filled with rubidium isbroken to heat metal rubidium, piping and glass cell, rubidium of gas ismade present within the piping and glass cell, then said glass cell iscooled, metal rubidium is precipitated as a solid into the cooledportion, xenon gas is introduced into the glass cell and closed, and theglass cell is cooled to solidify xenon within the glass cell.
 6. Aproducing apparatus of nuclear spin polarized xenon gas, comprisingmeans for heating a glass cell having solid rubidium and solid xenonfilled in the pressure reducing state of being absent in oxygen to begas xenon and gas-liquid mixed rubidium, and means for applying amagnetic field to the glass cell to irradiate a laser beam.
 7. Theproducing apparatus according to claim 6, further comprising means forintroducing xenon gas while taking out the produced nuclear spinpolarized xenon gas, and pressure regulating means for controlling saidoperation so that pressure may not drop.
 8. The producing apparatusaccording to claim 6 or 7, wherein a xenon gas supply device side ismade to be a primary side piping through a first air operate valve,piping extended up to a valve for introducing xenon gas into a glasscell is made to be a secondary side piping, branched pipings connectedto said primary side piping through a second air operate valve, one ofsaid branched pipings reaching a vacuum generator and the other reachinga valve on the xenon gas taking-out side of said glass cell, andpressure regulating means for regulating pressure introduced into theglass cell is provided on the primary side piping.
 9. A producingapparatus of a glass cell having solid rubidium and solid xenon filledin vacuum comprising: piping connected so that a chamber housingrubidium filled into a glass vessel and the glass cell are connected,means for vacuuming the piping, means for breaking glass having rubidiumfilled in, means for heating metal rubidium, piping and a glass cell,and means for cooling the glass cell and precipitating metal rubidium onthe cooled portion